It is known from the prior art to manufacture sub-micrometer periodic structures, such as photonic crystals, by means of e-beam-lithography. In fact e-beam-lithography is the only prior art method which can be utilized for the manufacturing of such structures, especially if aspect ratios of 1 to 200 and above need to be accomplished. However, e-beam-lithography is an expensive process which limits its field of application.
In U.S. Pat. No. 5,385,114 a method of preparing a photonic crystal is described in which the pores of a reticulated mesh are impregnated with a suitable liquid dielectric material which is then solidified. In order to introduce the dielectric material, the material of the mesh must have a much higher melting point than the dielectric material and so, for example, the material of the mesh is a metal. Thereafter, the mesh is dissolved using a suitable liquid chemical reactant to leave a porous dielectric material. The pores of the dielectric material have a different refractive index to the material itself, so a periodic structure made in this way would enable the material to function as a photonic crystal.
After the reticulated mesh has been removed, the pores in the dielectric material may be filled with a separate material that has a refractive index different to the refractive index of the dielectric material. In this document the method of pore filling is demonstrated using a random rather than a periodic metallic mesh but it is envisaged that a periodic metal mesh could be formed by freezing electrohydrodynamically generated metal droplets, by weaving a mesh of wires, by assembling small pieces or, by inference from the preamble, by drilling or reactive ion etching a slap of metal through a mask.
WO 99/09439 A1 shows a method of forming a photonic crystal material. The photonic crystal material has a 3-D periodic structure with a periodicity that varies on a length scale comparable to the wavelength of electromagnetic radiation. The 3-D periodic structure is produced by irradiating photosensitive material with electromagnetic radiation such that interference between radiation propagating in different directions within the sample gives rise to a 3-D periodic variation in intensity within the sample. Thereafter the irradiated material is developed to remove the less or more irradiated regions of the material to produce a structure having 3-D periodicity in the refractive index of the composite material. This method is limited to very special photo sensitive materials.
WO 99/41626 A1 shows an optical grating structure. The grating structure is arranged in a substrate containing a semiconductor material, so that light having a frequency within a particular frequency band cannot propagate in the grating structure. The grating structure comprises an arrangement of pores and a defective zone. The pores outside the defective zone are arranged in a periodical pattern and the periodical pattern is disturbed in the defective zone. The surface of the grating structure is provided with a conductive layer at least in the area of the detective zone. The grating structure is produced by electro chemical etching of n-doped silicon.
From “Microstructure and photoluminescence spectra of porous InP”, Aimin Liu, Institute of Physics Publishing, Nanotechnology 12 (2001) L1-L3, a method for electro chemical etching InP in known for the fabrication of porous InP. Quantum confinement effects taking place in nanometer-size semiconductor particles are used, i.e. quantum confinement effect induced photoluminescence emission can be observed. The microstructure of the porous layer strongly depends on the potential voltage applied on the InP electrode. Another method for producing porous semiconductors relying on electro chemical etching is known from DE 100 11 253 A1.
It is therefore an object of the present invention to provide for an improved method of forming a semiconductor component, such as an optical component.